Electrochemical recording of electric currents



Patented Apr. 21, 1936 UNITED STATES ELECTROCHEMICAL RECORDING OFELECTRIC CURRENTS Emil Glas, Vienna, Austria No Drawing. Application May3, 1933, Serial No. 669,278. In Austria May 4, 1932 1 Claim.

The present invention relates to electrochemical recording of electriccurrents of any kind; and has among its objects the production ofmaterial upon which the record may be made and a proc- 5 ess of making arecord of electric currents and of variations therein. A further objectof the invention is the production of impregnated or coated materialupon which the recording is to be made, which contains a reagent orreagents which will combine with the metal ions leaving the recordingelectrode to form immediately and directly an insoluble coloringsubstance. Other objects and advantages of the present invention areapparent or stated in the text below.

isted for recording electric currents, and vibrations therein whichmethods fundamentally may be classified into the two groups consideredbelow.

(1) Some reaction was used by which, when the current passed, a solublecolored product was produced. There were, however, serious drawbacks inthis method, the most important of g which are the comparatively lowsensitivity of the reaction, and the fact that the color turns paleunder the influence of air and light.

(2) These drawbacks were partly avoided by methods which are essentiallyfounded upon first forming an insoluble reaction product (a carriersubstance) and only thereafter coloring said reaction product. To thisgroup belongs especially the reaction between ferrous ions and potassiumferrocyanide which, as is well .known, primarily forms a colorlessprecipitate of ferrous ferro cyanide, which is only thereafter oxidizedinto colored ferric ferrocyanide. In order toobtain records of constantquality, it is not only necessary to keep constant the concentration ofthe soaking solution and the method of soaking, but 9 also to controlthe conditions under which the secondary coloring reaction is performed.Moreover, it is necessary that this primarily formed substance has anadsorption power as high as possible, for the colored substances areonly held fast by the adsorbing effect of the carrier substance. Thewhole accomplishment of this prior method recording therefore becomesvery complicated. The adsorbing effect is dependent only upon. thenature of the surface of the carrier substance. Therefore the color.will not be proportional to the intensity of the current, because thesecondary coloring reaction needs a certain time for completionwhile'the adsorbing power of the carrier substance decreases.

Heretofore several electrochemical methods ex- Contrary to all these oldmethods, the present invention, by the use of proper imbibing substancesand the electrochemical effect of the electrode recording the current,induces immediately (and without intermediate or catalytic reaction) acoloring reaction which gives a reaction product which is practicallyinsoluble and at the same time colored. This reaction takes placepractically instantaneously; and results in practically absolutesharpness of recording. Another important matter to be considered inchoosing the reactions is that they also must b'e fit for recording highfrequencies, like the highest musical audible frequencies. Therefore onehad to take into consideration the most sensitive reaction groups, whichat the same time satisfy the condition of an insoluble colored reactionproduct or precipitate. Another advantage obtained by the presentinvention is that the coloring reaction is not merely superficially doneand fixed like in the methods mentioned under 2, but that much more apenetrating effect of the coloring reaction together with an intensityof color (color tone) proportional to the current flow is obtained.Owing to the penetrating effect of the method of the present inventionthe resistance against mechanical stress by the electrode pin (pencil)is essentially increased. On account of the stability of the finalproducts, it is also perfectly impossible for the color to turn pale orfade. Since, regardless of whether reacting substances are brought inthe soaking solution by the electric current, or are produced fromcomponents present therein or whether by catalytic effect reactions areinduced, the quantitative yield per unit of time will be low and it isonly possible to increase the conductivity of the soaking solution to alimited extent, the sensitiveness of a reaction, which, as above menetioned, is of outstanding importance in the pres- .ent case, can beevaluated from two points of view. For the present purpose especiallythe test limit is important, i. e. the smallest quantity of substancewhich can be found by the reaction, no matter in what volume. on theother hand, the limiting concentration is less important. Therefore onehas to take into account especially such reactions, the test limit ofwhich is as low as possible. The sensitiveness is in many cases limitedby the visibleness of the final products. If the molecules are enlargedby bringing in weight increasing groups of atoms and the coloring effectis intensified by the addition of cbloring groups, this limit isextended. As also insolubility and stability are required, the number ofavailable reactions is considerably diminished. In the present inventionall these necessities are satisfled by the use of reactions which leadto the formation of inner complex. comr ounds. Compounds which have aring of five or six members are especially suitable, which compounds arecharacterized by high stability. In this group we find a series ofreactions which fully satisfy all conditions. The copper salt or thediamide oi thio-oxalic acid serves as illustrative. The copper is notonly by principal valencies linked to the two sulphur atoms, but also bysecondary valencies to the two Nil-groups.

Practical realization is extremely simple. The record ribbon is soakedwith a solution of the compound capable of reaction and is used forrecording either immediately or later on (in the latter case it iswetted again with some proper liquid). It ,necesasry, a reagentimproving the conductivity which also advances the reaction can beadded. Metallic ions are preferably introduced in known manner by theuse of a pin of the corresponding metal or of a proper alloy-mainly forreasons of solidity. The form of the pin is dependent on particularworking conditions.

Recording can be made on opaque material like paper or on transparentmaterial like cellophane, gelatine, etc. when a record ribbon ismentioned herein is always meant a sheet of the substance to beimpregnated in any form and not only in the form of a long narrowribbon.

The described method is explained by the following examples.

(1) The record ribbon is suitably impregnated with a solution (forexample alcoholic solution) of diamide of thio-oxalic acid. Forimproving the conductivity a salt can be added, for instance sodiumacetate, which at the same time advances the reaction by shifting theequilibrium in the solution in favor of the aciiorm of the diamid. Foranode one uses a copper or nickel pir. or a pin of silicon bronze(Cu-+0.05% Si) which by the action 01 the current goes into solution.The record is of black color. The slight original hue of the diamide caneasily be removed by subsequent washing in case it should be bothersome,without changing in the least the color of the lines. The highsensitiveness allows the highest speeds of recording.

(2) For soaking, a slightly acid (with acetic acid) or alkaline solutionof nitrous naphthol (nitrosonaphthol). 'For anode a cobalt pin is used.Here also the conductivity can be increased by the addition of salts.Otherwise, the process is the same as .with diamide of thio-oxalic acid.

I claim:

In the art of electro-chemical recording by means of a metallic stylusupon a sensitized base material of the type of paper, cellophane, andgelatin the step which comprises electr'o-chemically recording with ametallic stylus upon a sen.- sitized base material in which thesensitizing agent is chosen from the group consisting of the diamide ofthio-oxalic acid and nitrosonaphthol the metal stylus being one whoseions, formed as a result of the passage of the electric current throughthe stylus, form colored salts with said sensitizing materials, saidstylus containing a metal chosen from the group consisting of copper,nickel, and cobalt.

EMIL GLAS.

